Genetic variation, classification and ‘race’
Lynn B Jorde & Stephen P Wooding
Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, Utah 84112, USA
Nature Genetics 36, S28 – S33 (2004) Published online: ; | doi:10.1038/ng1435
New genetic data has enabled scientists to re-examine the relationship between human genetic variation and ‘race’. We review the results of genetic analyses that show that human genetic variation is geographically structured, in accord with historical patterns of gene flow and genetic drift. Analysis of many loci now yields reasonably accurate estimates of genetic similarity among individuals, rather than populations. Clustering of individuals is correlated with geographic origin or ancestry. These clusters are also correlated with some traditional concepts of race, but the correlations are imperfect because genetic variation tends to be distributed in a continuous, overlapping fashion among populations. Therefore, ancestry, or even race, may in some cases prove useful in the biomedical setting, but direct assessment of disease-related genetic variation will ultimately yield more accurate and beneficial information.
Figure 1: A neighbor-joining network of population similarities, based on the frequencies of 100 Alu insertion polymorphisms.
The network is rooted using a hypothetical ancestral group that lacks the Alu insertions at each locus. Bootstrap values are shown (as percentages) for main internal branches. (Because of the relatively small sample sizes of some individual populations, bootstrap values for terminal branches within main groups are usually smaller than those of the main branches, indicating less statistical support for terminal branches.) The population groups and their sample sizes are as follows: Africans (152): Alur, 12; Biaka Pygmy, 5; Hema, 18; Coriell Mbuti Pygmy, 5; a second sample of Mbuti Pygmy from the Democratic Republic of the Congo, 33; Nande, 17; Nguni, 14; Sotho/Tswana, 22; Kung (San), 15; Tsonga, 14. East Asians (61): Cambodian, 12; Chinese, 17; Japanese, 17; Malay, 6; Vietnamese, 9. Europeans (118): northern Europeans, 68; French, 20; Poles, 10; Finns, 20. South Indians (365): upper caste Brahmin, Kshatriya and Vysya, 81; middle caste Kapu and Yadava, 111; lower caste Relli, Mala and Madiga, 74; tribal Irula, Khonda Dora, Maria Gond and Santal, 99.
A neighbor-joining tree of individual similarities, based on 60 STR polymorphisms, 100 Alu insertion polymorphisms, and 30 restriction site polymorphisms. The percentage of shared alleles was calculated for all possible pairs of individuals, and a neighbor-joining tree was formulated using the PHYLIP software package. African individuals are shown in blue, European individuals in green and Asian individuals in orange.
(a) Results of applying the structure program to 100 Alu insertion polymorphisms typed in 107 sub-Saharan Africans, 67 East Asians and 81 Europeans. Individuals are shown as dots in the diagram. Three clusters appear in this diagram; a cluster membership posterior probability of 100% would place an individual at an extreme corner of the diagram.
(b) A second application of the structure program, using the individuals shown in a as well as 263 members of caste populations from South India. Adapted from ref. 32.
A neighbor-joining tree formulated using the same methods as in Figure 2, based on polymorphisms in the 14.4-kb gene AGT.
A total of 246 sequence variants, including 100 singletons, were observed. The 368 European, Asian and African individuals are described further in ref. 54.
Author’s conclusion: “Race remains an inflammatory issue, both socially and scientifically. Fortunately, modern human genetics can deliver the salutary message that human populations share most of their genetic variation and that there is no scientific support for the concept that human populations are discrete, nonoverlapping entities. Furthermore, by offering the means to assess disease-related variation at the individual level, new genetic technologies may eventually render race largely irrelevant in the clinical setting. Thus, genetics can and should be an important tool in helping to both illuminate and defuse the race issue.”
Note by RK ” there is no scientific support for the concept that human populations are discrete, nonoverlapping entities.” – Outside of racist groups, no one, let alone scientists, make such a claim. This article does not debunk the idea that biological groups/races/clades for humans exists: It clearly proves that such groups exists, and shows it in precise detail. However, this data can also debunk racial claims made from people using non-scientific definitions of the word “race”.
When scientists use words like “race”, “populations” or “clades”, these words have precise meanings. Every discovery in biology and evolution over the last 200 years has clearly shown that the basic concept of biological groups has to exist. All forms of life have family trees that develop in ways that can be represented by cladograms, and those cladograms show evolutionary phylogenies.
“A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. Using a phylogeny, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny — all of the organisms on that pruned branch make up a clade.”